Heat packs utilizing supercooled aqueous salt solutions have been used for some time for the treatment of soreness of muscles of athletes and sportsman in localized areas. From the simple hot water bottle we have progressed upward to the use of supercooled aqueous salt solutions wherein the temperatures can be controlled as well as the duration of the heat given off. Various solutions such as sodium acetate and calcium nitrate tetrahydrate are examples of such solutions.
Various techniques of initiating crystallization have been recommended, including inserting a crystal of material into the supercooled solution, and scraping some metal inside the container to introduce impurities into the supercooled solution. Examples of these techniques are disclosed in the following U.S. Pat. Nos. 1,433,010; 2,289,425; 2,220,777; 3,093,308; 4,077,390; and 4,572,158. U.S. Pat. No. 1,915,523 discloses the introduction of air into the solution by means of a valve. This complicated method involves the use of both hands to manipulate the valve.
U.S. Pat. No. 5,305,733 discloses a trigger for a heat pack. The trigger pierces a flexible container filled with a supercooled salt solution, wherein the trigger has a piercing means and a sealing means. The trigger allows air to be admitted, initiating precipitation and causing the pack to exotherm.
A variety of techniques have also been directed to the problem of saddlebagging when the heat pack is in use. U.S. Pat. No. 3,301,250 discloses a heat pack that uses vermiculite, iron particles, ammonium chloride, wetting agent and water to provide such a pack. When air is admitted to the mixture, the iron filings oxidize and thereby produce heat. This fairly complicated mixture provides a lumpy heat pack.
U.S. Pat. No. 3,951,127 discloses a flexible heating pack that contains a foam insulation as an external layer to the exotherming chemicals. The foam does not come in contact with the supercooled salt solution.
U.S. Pat. No. 4,106,477 discloses a water activated therapeutic moist heat pad having outer porous water retaining layers which enclose an inner layer of distributed heat generating cells and an associated water retaining absorbent inner porous layer. The inner layers are covered by an outer sponge-like layer to form a composite pad structure capable of retaining a sufficient amount of water for the transfer of heat. The device described is an that of a heat pack using electrochemical cells provided with discrete electrically located shorts to generate internal heating of the cell when it is activated by the addition of water. This device is far more complicated than that claim in the present application. It fails to address the problem of saddlebagging that is remedied in the present invention.
The present invention provides a simple device that is easily manufactured and the trigger is easily activated. Of particular advantage is that the heat pack of the present invention can be initiated using one hand. Of further advantage is that a temperature indicator can be attached to the heat pack to indicate the appropriate temperature. A final advantage is that the heat pack optionally contains a foam rubber pad inside the flexible container which provides additional support, and prevents saddlebagging when the pack is in use. This option is particularly useful in larger heat packs which can be used to place premature babies on and to warm them.